Lens and light emitting module for surface illumination

ABSTRACT

An exemplary embodiment of the present invention discloses a light-emitting module including a circuit board, a light-emitting device disposed on the circuit board, and a lens disposed on the circuit board and configured to distribute light emitted from the light emitting device. The lens includes a concave portion having an incidence surface configured to receive incident light emitted from the light-emitting device, and the light emitting device is disposed within the concave portion of the lens.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional PatentApplication No. 61/720,105, filed on Oct. 30, 2012, which is herebyincorporated by reference for all purposes as if fully set forth herein.

BACKGROUND

1. Field

Exemplary embodiments of the present invention relate to a lightemitting module, and more particularly, to a lens for surfaceillumination and a light emitting module for surface illumination havingthe same.

2. Discussion of the Background

In general, a light emitting module for backlighting a liquid crystaldisplay or a light emitting module for surface illumination, which isused in a surface illumination apparatus, includes a light emittingdevice mounted on a circuit board, and a lens for distributing lightemitted from the light limiting device at a wide angle. By uniformlydistributing the light emitted from the light emitting device using thelens, it is possible to uniformly irradiate a wide area with a smallnumber of light emitting devices.

FIGS. 1A and 1B are respectively sectional and perspective viewsschematically illustrating a conventional light emitting module and aconventional lens.

Referring to FIGS. 1A and 1B, the light emitting module includes acircuit board 100, a light emitting device 200 and a lens 300. Thecircuit board 100 is a printed circuit board on which a circuit forsupplying electric power to the light emitting device 200 is formed.

The light emitting device 200 generally includes a light emitting diode(LED) chip 210, a molding portion 230 covering the LED chip 210, and apackage substrate 250. The molding portion 230 may include a phosphorused for converting the wavelength of light emitted from the LED chip210 and have a lenticular shape. The package substrate 250 may have arecess for mounting the LED chip 210 therein. The light emitting device200 is electrically connected to the circuit board 100.

Meanwhile, the lens 300 includes a lower surface 310 and an uppersurface 350, and may also include a flange 370 and leg portions 390. Theleg portions 310 are attached onto the circuit board 100, so that thelens 300 is disposed above the light emitting device 200. As shown inFIG. 1B, the leg portions 310 are usually comprised of three legportions that are disposed at apexes of a regular triangle.

The lens 300 has an incidence surface 330 on which light from the lightemitting device 200 is incident, and an exit surface 350 from which thelight exits. The incidence surface 330 is an inner surface of ashell-shaped concave portion 320 formed on the lower surface 310 of thelens 300. Since the concave portion 320 is disposed above the lightemitting device 200, light emitted from the light emitting device 200 isincident into the lens 300 through the incidence surface 330. The exitsurface 350 allows the light incident into the lens 300 to exit over awide viewing angle.

In the conventional light emitting module, the light emitted from thelight emitting device 200 is distributed through the lens 300, so thatuniform light can be achieved over a wider area. However, since thelight emitting device 200 mounted on the circuit board 100 employs thepackage substrate 250, the size of the light emitting device 200 isrelatively large. Accordingly, the entrance and height of the concaveportion 320 for forming the incidence surface 330 of the lens 300 arealso relatively larger, and as a result, it is difficult to slim thelens 300. Further, since the viewing angle of the light emitted from thelight emitting device 200 is relatively narrow, there is a limitation ondistribution of light through the lens 300.

Furthermore, since the light emitting device 200 is positioned beneaththe lower surface 310 of the lens 300, a portion of the light emittedfrom the light emitting device 200 is not incident into the lens 300 butis likely to be lost beneath the lower surface 310 of the lens 300.

The above information disclosed in this Background section is only forenhancement of understanding of the background of the invention andtherefore it may contain information that does not form any part of theprior art nor what the prior art may suggest to a person of ordinaryskill in the art.

SUMMARY OF THE INVENTION

Exemplary embodiments of the present invention provide a technique forslimming a lens and a light emitting module for surface illumination.

Exemplary embodiments of the present invention also provide a lens and alight emitting module, which can reduce loss of light emitted from alight emitting device.

Exemplary embodiments of the present invention also provide a lightemitting module which can provide uniform light over a wide area byemploying a light emitting device suitable for surface illumination.

Additional features of the invention will be set forth in thedescription which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention.

A light emitting module according to an exemplary embodiment of thepresent invention includes a circuit board, a light emitting devicedisposed on the circuit board, and a lens disposed on the circuit board,the lens configured to distribute light emitted from the light-emittingdevice. The lens includes a concave portion having an incidence surfaceconfigured to receive incident light emitted from the light-emittingdevice, and the light emitting device is disposed within the concaveportion of the lens.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention, andtogether with the description serve to explain the principles of theinvention.

FIG. 1A is a sectional view illustrating a conventional light emittingmodule.

FIG. 1B is a perspective view of a lens employed in the conventionallight emitting module.

FIG. 2A is a sectional view illustrating a light emitting moduleaccording to an exemplary embodiment of the present invention.

FIG. 2B is a perspective view of a lens employed in the light emittingmodule according to an exemplary embodiment of the present invention.

FIG. 2C is a schematic view illustrating the shape of a concave portionof the lens according to an exemplary embodiment of the presentinvention.

FIG. 2D is an enlarged sectional view of a portion of the lens employedin the light emitting module according to an exemplary embodiment of thepresent invention.

FIG. 3 shows sectional views illustrating different variations of thelens.

FIG. 4 is a sectional view illustrating a further variation of the lens.

FIG. 5 is a sectional view illustrating a still further variation of thelens.

FIG. 6 is a schematic sectional view illustrating a light emittingdevice according to an exemplary embodiment of the present invention.

FIGS. 7( a), 7(b), 8(a), 8(b), 9(a), 9(b), 10(a), 10(b), 11(a), 11(b),and 12 are views illustrating a method of fabricating a light emittingdiode (LED) chip that can be used in the light emitting device accordingto an exemplary embodiment of the present invention, wherein (a) of eachof these figures shows a plan view and (b) thereof shows a sectionalview taken along line A-A.

FIGS. 13( a) and (b) are graphs showing directivity distributions of aconventional LED package 200 and a flip-chip type LED chip having aconformal coating layer according to an exemplary embodiment of thepresent invention, respectively.

FIGS. 14( a) and (b) are graphs showing directivity distributions of alight emitting module using the conventional LED package and a lightemitting module using the flip-chip type LED chip having the conformalcoating layer according to an exemplary embodiment of the presentinvention, respectively.

FIGS. 15( a), (b) and (c) are schematic views illustrating exitdirections of light depending on various slopes of an inclinationsurface of a lower surface of the lens.

FIGS. 16( a) and (b) are graphs showing exit angles of light dependingon various slopes of the inclination surface of the lower surface of thelens.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

The invention is described more fully hereinafter with reference to theaccompanying drawings, in which embodiments of the invention are shown.This invention may, however, be embodied in many different forms andshould not be construed as limited to the embodiments set forth herein.Rather, these embodiments are provided so that this disclosure isthorough, and will fully convey the scope of the invention to thoseskilled in the art. In the drawings, the size and relative sizes oflayers and regions may be exaggerated for clarity. Like referencenumerals in the drawings denote like elements.

It will be understood that when an element or layer is referred to asbeing “on” or “connected to” another element or layer, it can bedirectly on or directly connected to the other element or layer, orintervening elements or layers may be present. In contrast, when anelement is referred to as being “directly on” or “directly connected to”another element or layer, there are no intervening elements or layerspresent. It will be understood that for the purposes of this disclosure,“at least one of X, Y, and Z” can be construed as X only, Y only, Zonly, or any combination of two or more items X, Y, and Z (e.g., XYZ,XYY, YZ, ZZ).

Spatially relative terms, such as “beneath”, “below”, “lower”, “above”,“upper” and the like, may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. For example, if the device in thefigures is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the exemplary term “below” can encompass both anorientation of above and below. The device may be otherwise oriented(rotated 90 degrees or at other orientations) and the spatially relativedescriptors used herein interpreted accordingly.

FIG. 2A is a sectional view illustrating a light emitting moduleaccording to an exemplary embodiment of the present invention. FIG. 2Bis a perspective view of a lens 300 a of the light emitting module. FIG.2C is a schematic view illustrating a concave portion 320 of the lens300 a. FIG. 2D is an enlarged sectional view illustrating of a portionof a lower surface 310 of the lens 300 a.

Referring to FIG. 2A, the light emitting module includes a circuit board100 a, a light emitting device 200 a and a lens 300 a. The lightemitting module may further include a reflective sheet 110.

The circuit board 100 a is a printed circuit board on which a circuitpattern is formed. Here, it is shown that one light emitting device 200a is mounted on the circuit board 100 a. However, a plurality of lightemitting devices 200 a may be arranged on the circuit board 100 a, andthe lens 300 a may be disposed above each of the light emitting devices200 a.

Unlike a conventional light emitting diode (LED) package, the lightemitting device 200 a does not have a chip-mounting member for mountingan LED chip, and is directly mounted on the circuit board 100 a by flipbonding without using a bonding wire. That is, the circuit board 100 aserves as a chip-mounting member for mounting an LED chip. Since thelight emitting device 200 a does not use a bonding wire, the lightemitting device 200 does not require a molding portion for protectingthe wire. A light emitting device 200 a according to an exemplaryembodiment of the present invention will be described in detail laterwith reference to FIG. 6.

The reflective sheet 110 is positioned between the lens 300 a and thecircuit board 100 a. A white reflective material with high reflectancemay be coated on the reflective sheet 110 so that the reflective sheet110 can reflect light in a wide range of wavelengths of a visibleregion. The reflective sheet 110 reflects light, which travels towardthe circuit board 100 a, into the lens 300 a.

The lens 300 a includes a lower surface 310 and an upper surface 330,and may further include a flange 370 and leg portions 390. The lowersurface 310 includes a concave portion 320, a flat surface 310 asurrounding the concave portion 320, and an inclination surface 310 bsurrounding the flat surface 310 a.

The concave portion 320 defines an incidence surface 330 through whichlight emitted from the light emitting device 200 a is incident into thelens 300 a. That is, the incident surface 330 is an inner surface of theconcave portion 320. The incidence surface 330 includes a side surface330 a and an upper end surface 330 b. The concave portion 320 has ashape narrowing as the concave portion 320 approaches upward from theentrance thereof. The side surface 330 a may be an inclination surfacehaving a constant slope from the entrance to the upper end surface 330b. Alternatively, the side surface 330 a may be an inclination surfaceof which slope decreases from the entrance to the upper end surface 330b. That is, as shown in FIG. 2C, the side surface 330 a is shown as astraight line or an upwardly convex curve in a vertical sectional view.

The light emitting device 200 a is disposed substantially inside theconcave portion 320. To this end, the width W1 of the entrance of theconcave portion 320 is greater than the width w of the light emittingdevice 200 a. The width W1 of the entrance of the concave portion 320may be two times or less greater than the width w of the light emittingdevice 200 a. In exemplary embodiments of the present invention, thelight emitting device 200 a has a relatively smaller size as comparedwith the conventional light emitting device 200, and thus, it isrequired to precisely align the light emitting device 200 a and the lens300 a. Therefore, the width W1 of the entrance of the concave portion320 is made to be no greater than two times than the width w of thelight emitting device 200 a, so that it is possible to preventmisalignment between the lens 300 a and the light emitting device 200 a.Further, since the light emitting device 200 a becomes closer to theincidence surface 330, it is possible to reduce light escaping outsidethe concave portion 320. Particularly, the width of the entrance of theconcave portion 320 may be no more than 3 mm or no more than 2 mm. Sincethe light emitting device 200 a is disposed within the concave portion320, most of the light emitted from the light emitting device 200 a canbe incident into the lens 300 a, thereby reducing loss of light beneatha lower surface 310 of the lens 300 a.

Meanwhile, the upper end surface 330 b of the incidence surface 320 hasa flat shape. The width W2 of the upper end surface 330 b is smallerthan the width W1 of the entrance and also smaller than the width w ofthe light emitting device 200 a. The width W2 of the upper end surface330 b may be determined so that the angle α defined by a central axis ofthe concave portion 320 and a straight line connecting from the centerof the entrance of the concave portion 320 to an edge of the upper endsurface 330 b is at least 3 degrees, preferably no less than 6 degrees.In the light emitted from the light emitting device 200 a, light havinga viewing angle in a range of +15 to −15 degrees is caused to beincident on at least the upper end surface 330 b, thereby improving thedistribution of light.

The upper end surface 330 b prevents a substantial change in directivitydistribution of light exiting outside of the lens 300 a from occurringwhen the central axes of the light emitting device 200 a and the lens300 a are not precisely aligned.

Meanwhile, the height H of the concave portion 320 may be adjusteddepending on the viewing angle of the light emitting device 200 c, theshape of the upper surface 350 of the lens 300 a, a desired directivitydistribution of light, and the like. However, in this embodiment, theheight H of the concave portion 320 may have a relatively smaller valueas compared with the conventional lens, since the width W1 of theentrance of the concave portion 320 decreases. Particularly, the heightH of the concave portion 320 may be smaller than the thickness of theflange 370.

Referring back to FIG. 2A, the upper surface 350 of the lens 300 a has ashape for distributing the light incident into the lens 300 a so as tohave a wide directivity distribution. For example, the upper surface 350of the lens 300 a may have a concave surface 350 a positioned close tothe central axis of the lens 300 a and a convex surface 350 b continuingfrom the concave surface 350 a. The concave surface 350 a allows lighttraveling toward the central axis of the lens 300 a to be distributedoutwardly, and the convex surface 350 b increases the amount of lightexiting outside the central axis of the lens 300 a.

Meanwhile, the flange 370 connects the upper and lower surfaces 350 and310 to each other and defines the external size of the lens 300 a.Concavo-convex patterns may be formed on a side surface of the flange370 and the lower surface 310. Meanwhile, the leg portions 390 of thelens 300 a are coupled to the circuit board 100 a so as to fix the lens300 a thereto. Respective tips of the leg portions 390 may be bonded tothe circuit board 100 a, for example, by an adhesive, or may be fittedinto holes formed in the circuit board 100 a.

As shown in FIG. 2B, the leg portions 390 may be comprised of four legportions. However, the leg portions 390 may be comprised of three legportions, as known in the related art. The leg portions 390 may beformed on the inclination surface 310 b as shown in FIG. 2D.

Referring to FIGS. 2A and 2D, the lower surface 310 of the lens 300 ahas the flat surface 310 a surrounding the concave portion 320, and theinclination surface 310 b surrounding the flat surface 310 a. The flatsurface 310 a is in close contact with the circuit board 100 a orreflective sheet 110, and thus, it is possible to prevent loss of lightat the lower surface 310 of the lens 300 a. In FIG. 2D, the radius ofthe lens 300 a is denoted by d/2, the length of the flat surface 310 afrom the incidence surface 330 a to the inclination surface 310 b isdenoted by b0, and the radial length of the inclination surface 310 b isdenoted by bx.

The inclination surface 310 b is inclined upward at an inclination angleβ with respect to the flat surface 310 a. The inclination surface 310 bcontinues up to the side surface of the lens 300, e.g., the side surfaceof the flange 370. Therefore, the side surface of the lens 300 a ispositioned at a height h with respect to the flat surface 310 a. Theinclination angle β of the inclination surface 310 b is preferably lessthan 10 degrees. This will be described in detail later with referenceto FIGS. 15 and 16. With the use of the inclination surface 310 b, it ispossible to reduce loss of light due to total internal reflection insidethe lens 300 a and to distribute light with a wide directivitydistribution.

FIG. 3 shows sectional views illustrating different variations of thelens. Here, different variations of the concave portion 320 of FIG. 1will be described.

In FIG. 3( a), a portion near the central axis C of the lens 300 a inthe upper end surface 330 b described with reference to FIG. 1 forms adownwardly convex surface. Light incident toward the central axis C canbe primarily controlled by this convex surface.

FIG. 3( b) is similar to FIG. 3( a) but is different from FIG. 3( a) inthat a surface perpendicular to the central axis C in the upper endsurface of FIG. 3( a) is formed to be upwardly convex. Upwardly anddownwardly convex surfaces are mixed in the upper end surface, and thus,it is possible to reduce a change in the directivity distribution oflight due to an alignment error between the light emitting device andthe lens.

In FIG. 3( c), a portion near the central axis C in the upper endsurface 330 b described with reference to FIG. 1 forms an upwardlyconvex surface. Light toward the central axis C can be furtherdistributed by this convex surface.

FIG. 3( d) is similar to FIG. 3( c) but is different from FIG. 3( c) inthat the surface perpendicular to the central axis C in the upper endsurface of FIG. 3( c) is formed to be downwardly convex. Upwardly anddownwardly convex surfaces are mixed in the upper end surface, and thus,it is possible to reduce a change in the directivity distribution oflight due to an alignment error between the light emitting device andthe lens.

FIG. 4 is a sectional view illustrating a further variation of the lensaccording to an exemplary embodiment of the present invention.

Referring to FIG. 4, a light-scattering pattern 330 c is formed on theupper end surface 330 b. The light-scattering pattern 330 c may beformed as a concavo-convex pattern.

Generally, relatively much light flux is concentrated near the centralaxis of the lens. Moreover, in the exemplary embodiments of the presentinvention, the upper end surface 330 b is a surface perpendicular to thecentral axis, and thus, light flux can be further concentrated near thecentral axis. Thus, the light-scattering pattern 330 c is formed on theupper end surface 330 b, thereby distributing the light flux near thecentral axis. Thus, even though the central axes of the light emittingdevice 200 a and the lens 300 a are misaligned, it is possible to reduceinfluence of the misalignment on the directivity distribution of light.Accordingly, an alignment tolerance between the light emitting device200 a and the lens 300 a is increased.

FIG. 5 is a sectional view illustrating a still further variation of thelens.

Referring to FIG. 5, the lens 400 a according to this variation isgenerally similar to the lens 300 a described with reference to FIGS. 2Ato 2D but is different from the lens 300 a in view of the shape of anupper surface 450 and the positions of leg portions 490. That is,instead of the concave surface 350 a in FIG. 2A, a relatively flatsurface 450 a is disposed near the central axis of the lens 400 a, and aconvex surface 450 b continues outwardly from the flat surface 450 a.The leg portions 490 are disposed near a side surface of the lens 400 a.

The shape of the lens may be variously modified in consideration of adesired directivity distribution of light, and the like.

FIG. 6 is a schematic sectional view illustrating a light emittingdevice 200 a according to an exemplary embodiment of the presentinvention.

Referring to FIG. 6, the light emitting device 200 a includes an LEDchip 210 and a wavelength conversion layer 240. The LED chip 210includes a substrate 211 and a semiconductor stack 213, and may furtherinclude electrode pads 215 a and 215 b.

The LED chip 210 is a flip chip and has the electrode pads 215 a and 215b positioned at a lower portion of the LED chip 210. The width w of theLED chip 210 may be in a range of about 0.7 to 1.5 mm.

The substrate 211 may be a growth substrate used for growing asemiconductor layer, for example, a sapphire substrate or galliumnitride (GaN) substrate. Particularly, in a case where the substrate 211is a sapphire substrate, refractive indices gradually decrease in theorder of the semiconductor stack 213, the sapphire substrate 211 and thewavelength conversion layer 240, thereby improving light extractionefficiency. In a specific embodiment, the substrate 211 may be omitted.

The semiconductor stack 213 is formed of a GaN-based compoundsemiconductor and can emit ultraviolet or blue light.

The LED chip 210 is mounted directly on the circuit board 100 a. The LEDchip 210 is connected directly to a printed circuit on the circuit board100 a by flip bonding without using a bonding wire. In an exemplaryembodiment of the present invention, a wire is not used when the LEDchip is bonded to the circuit board 100 a. Hence, a molding portion forprotecting a wire is not required, and it is also not required to removea portion of the wavelength conversion layer 240 so as to expose abonding pad. Thus, employing the flip-chip type LED chip 210 enableselimination of a phenomenon such as color deviation or luminance specksand simplification of a module fabricating process as compared with anLED chip using a bonding wire.

A flip-chip type LED chip according to an exemplary embodiment of thepresent invention will be described in detail later with reference toFIGS. 7 to 12.

Meanwhile, the wavelength conversion layer 240 covers the LED chip 210.As shown in FIG. 6, a conformal-coated wavelength conversion layer 240,e.g., a phosphor layer, can be formed on the LED chip 210 and performwavelength conversion of light emitted from the LED chip 210. Thewavelength conversion layer 240 is coated on the LED chip 210, and maycover top and side surfaces of the LED chip 210. In a specificembodiment, the wavelength conversion layer 240 may cover only the topsurface of the LED chip 210. Light with various colors can be realizedusing the light emitted from the LED chip 210 and the wavelengthconversion layer 240. Particularly, mixed light such as white light canbe realized.

In this embodiment, the conformal-coated wavelength conversion layer 240may be previously formed on the LED chip 210 so as to be mountedtogether with the LED chip 210 on the circuit board 100 a.

Hereinafter, a method of fabricating the LED chip 210 will be describedfor better understanding of the LED chip 210.

FIGS. 7 to 11 are views illustrating a method of fabricating a flip-chiptype LED chip according to an exemplary embodiment of the presentinvention, wherein (a) of each of these figures is a plan view and (b)thereof is a sectional view taken along line A-A.

Referring to FIG. 7, a first conductive semiconductor layer 23 is formedon a growth substrate 21, and a plurality of mesas M spaced apart fromone another is formed on the first conductive semiconductor layer 23.Each of the plurality of mesas M includes an active layer 25 and asecond conductive semiconductor layer 27. The active layer 25 ispositioned between the first and second conductive semiconductor layers23 and 27. Meanwhile, reflective electrodes 30 are positioned on theplurality of mesas M, respectively.

The plurality of mesas M may be formed by growing an epitaxial layerincluding the first conductive semiconductor layer 23, the active layer25 and the second conductive semiconductor layer 27 on the growthsubstrate 21 using a metal organic chemical vapor growth technique orthe like, and then by patterning the second conductive semiconductorlayer 27 and the active layer 25 so that the first conductivesemiconductor layer 23 is exposed. Side surfaces of the plurality ofmesas M may be formed to be inclined using a technique such asphotoresist reflow. The profile of the inclined side surface of the mesaM improves the extraction efficiency of light generated in the activelayer 25.

The plurality of mesas M may have an elongated shape extending inparallel with one another in one direction as shown in this figure. Sucha shape simplifies formation of the plurality of mesas M having the sameshape in a plurality of chip regions on the growth substrate 21.

Meanwhile, although the reflective electrodes 30 may be formed on therespective mesas M after the plurality of mesas M are formed, thepresent invention is not limited thereto. That is, the reflectiveelectrodes 30 may be previously formed on the second conductivesemiconductor layer 27 before the mesas M are formed after the secondconductive semiconductor layer 27 is formed. The reflective electrode 30covers most of the top surface of the mesa M, and has a shape generallyidentical to the planar shape of the mesa M.

Each of the reflective electrodes 30 includes a reflective layer 28 andmay further include a barrier layer 29. The barrier layer 29 may covertop and side surfaces of the reflective layer 28. For example, thebarrier layer 29 may be formed to cover the top and side surfaces of thereflective layer 28 by forming a pattern of the reflective layer 28 andthen forming the barrier layer 29 thereon. For example, the reflectivelayer 28 may be formed by vapor-depositing and patterning an Ag, Agalloy, Ni/Ag, NiZn/Ag or TiO/Ag layer. The barrier layer 29 may beformed of a layer of Ni, Cr, Ti, Pt, Rd, Ru, W, Mo, TiW or compositesthereof, and prevents a metallic material of the reflective layer 28from being diffused or contaminated.

After the plurality of mesas M has been formed, edges of the firstconductive semiconductor layer 23 may be etched. Accordingly, portionsof an upper surface of the substrate 21 can be exposed. The side surfaceof the first conductive semiconductor layer 23 may also be formedinclined.

The plurality of mesas M may, as shown in FIG. 7, be formed to berestricted only within and positioned in an upper region of the firstconductive semiconductor layer 23. That is, the plurality of mesas M maybe positioned in the form of islands on the upper region of the firstconductive semiconductor layer 23. Alternatively, as shown in FIG. 12,the mesas M extending in one direction may be formed to reach an upperedge of the first conductive semiconductor layer 23. That is, one edgeof the lower surface of each of the plurality of mesas M corresponds toone edge of the first conductive semiconductor layer 23. Accordingly,the upper surface of the first conductive semiconductor layer 23 isdivided by the plurality of mesas M.

Referring to FIG. 8, a lower insulating layer 31 is formed to cover theplurality of mesas M and the first conductive semiconductor layer 23.The lower insulating layer 31 has openings 31 a and 31 b for allowingelectrical connections to the first and second conductive semiconductorlayers 23 and 27 in a specific region. For example, the lower insulatinglayer 31 may have openings 31 a for exposing the first conductivesemiconductor layer 23 therethrough and openings 31 b for exposing thereflective electrodes 30 are exposed therethrough.

The openings 31 a may be positioned in regions between the mesas M andnear edges of the substrate 21, and may have an elongated shapeextending along the mesas M. The openings 31 b are restricted only onand positioned at upper portions of the respective mesas M, and arepositioned to be biased toward the same side of ends of the mesas M.

The lower insulating layer 31 may be formed of a layer of oxides such asSiO₂, a layer of nitrides such as SiNx, or a layer of insulativematerials such as SiON or MgF₂ using a technique such as chemical vapordeposition (CVD). The lower insulating layer 31 may be formed to have asingle-layered structure but is not limited thereto. That is, the lowerinsulating layer 31 may be formed to have a multi-layered structure.Further, the lower insulating layer 31 may be formed of a distributedBragg reflector (DBR) in which layers of materials with low and highrefractive indices are alternately laminated. For example, layers ofdielectrics such as SiO₂/TiO₂ or SiO₂/Nb₂O₅ are laminated to form aninsulating reflective layer having high reflectance.

Referring to FIG. 9, a current-spreading layer 33 is formed on the lowerinsulating layer 31. The current-spreading layer 33 covers the pluralityof mesas M and the first conductive semiconductor layer 23. Thecurrent-spreading layer 33 has openings 33 a which are positionedrespectively in upper regions of the mesas M and expose the reflectiveelectrodes therethrough. The current-spreading layer 33 may be inohmic-contact with the first conductive semiconductor layer 23 throughthe openings 31 a of the lower insulating layer 31. Thecurrent-spreading layer 33 is insulated from the plurality of mesas Mand the reflective electrodes 30 by the lower insulating layer 31.

Each of the openings 33 a of the current-spreading layer 33 has an arealarger than that of each of the openings 31 b of the lower insulatinglayer 31 so as to prevent the current-spreading layer 33 from beingconnected to the reflective electrodes 30. Thus, side walls of theopenings 33 a are positioned on the lower insulating layer 31.

The current-spreading layer 33 is formed on the almost entire region ofthe substrate 31 except for the openings 33 a. Thus, an electricalcurrent can be easily distributed through the current-spreading layer33. The current-spreading layer 33 may include a highly-reflective metallayer such as an Al layer, and the highly-reflective metal layer may beformed on an adhesion layer of Ti, Cr or Ni. A protective layer with asingle-layered or composite-layered structure of Ni, Cr, Au and the likemay be formed on the highly-reflective metal layer. Thecurrent-spreading layer 33 may have a multi-layered structure ofTi/Al/Ti/Ni/Au.

Referring to FIG. 10, an upper insulating layer 35 is formed on thecurrent-spreading layer 33. The upper insulating layer 35 has openings35 b for exposing the respective reflective electrodes 30 therethrough,together with an opening 35 a for exposing the current-spreading layer33 therethrough. The opening 35 a may have a shape that is elongated ina direction perpendicular to the direction of the length of the mesa M,and has an area relatively larger than those of the openings 33 b. Theopenings 35 b expose the reflective electrodes 30 that are exposedthrough the openings 33 a of the current-spreading layer 33 and theopenings 31 b of the lower insulating layer 31. The openings 35 b mayhave areas narrower than those of the openings 33 a of thecurrent-spreading layer 33 but wider than those of the openings 31 b ofthe lower insulating layer 31. Accordingly, the side walls of theopenings 33 a of the current-spreading layer 33 can be covered by theupper insulating layer 35.

The upper insulating layer 35 may be formed using an insulating layer ofoxides, an insulating layer of nitrides, or a mixed or alternating layerthereof; or using a polymer such as polyimide, Teflon or parylene.

Referring to FIG. 11, first and second pads 37 a and 37 b are formed onthe upper insulating layer 35. The first pad 37 a is connected to thecurrent-spreading layer 33 through the opening 35 a of the upperinsulating layer 35, and the second pad 37 b is connected to thereflective electrodes 30 through the openings 35 b of the upperinsulating layer 35. The first and second pads 37 a and 37 b may be usedas pads for connecting bumps or for applying a surface mountingtechnology (SMT) in order to mount LEDs on a circuit board or the like.

The first and second pads 37 a and 37 b may be formed together in thesame process. For example, the first and second pads 37 a and 37 b maybe formed using a photolithography technique or lift-off technique. Thefirst and second pads 37 a and 37 b may include, for example, anadhesion layer of Ti, Cr, Ni or the like, and a highly-conductive metallayer of Al, Cu, Ag, Au or the like. The first and second pads 37 a and37 b may be formed such that their ends are positioned on the sameplane. Thus, LED chips can be flip-bonded on the respective conductivepatterns formed at the same height on the circuit board 100 a to 100 d.In addition, the first and second pads 37 a and 37 b may be formed tohave the same shape and size, and thus, flip-chip bonding can be easilyperformed.

Subsequently, the growth substrate 21 is divided on an individual LEDchip basis, thereby completing LED chips. The growth substrate 21 may beremoved from the LED chips before or after it is divided on theindividual LED chip basis.

Hereinafter, the structure of an LED chip according to an exemplaryembodiment of the present invention will be described in detail withreference to FIG. 11.

The LED chip includes a first conductive semiconductor layer 23, mesasM, reflective electrodes 30 and a current-spreading layer 33, and mayfurther include a growth substrate 21, a lower insulating layer 31, anupper insulating layer 35 and first and second pads 37 a and 37 b.

The substrate 21 may be a growth substrate for growing a GaN-basedepitaxial layer, e.g., a sapphire substrate or GaN substrate. Thesubstrate 21 is, for example, a sapphire substrate, and may have athickness of 200 μm or more and preferably 250 μm or more.

The first conductive semiconductor layer 23 is continuous, and theplurality of mesas M is positioned to be spaced apart from one anotheron the first conductive semiconductor layer 23. Each of the mesas Mincludes an active layer 25 and a second conductive semiconductor layer27, as described with reference to FIG. 7, and has an elongated shapeextending in one direction. Here, the mesa M has a stack of GaN-basedcompound semiconductors. The mesa M may be restricted only within andpositioned in an upper region of the first conductive semiconductorlayer 23, as shown in FIG. 7. Alternatively, the mesa M may extend up toedges of an upper surface of the first conductive semiconductor layer 23in one direction, as shown in FIG. 12, and thus, can partition the uppersurface of the first conductive semiconductor layer 23 into a pluralityof regions. Accordingly, it is possible to prevent an electrical currentfrom being concentrated near corners of the mesas M, thereby furtherreinforcing current-distributing performance.

The reflective electrodes 30 are positioned on the plurality of mesas M,respectively, and are in ohmic contact with the second conductivesemiconductor layer 27. Each of the reflective electrodes 30 may includea reflective layer 28 and a barrier layer 29, and the barrier layer 29may cover top and side surfaces of the reflective layer 28, as describedin FIG. 7. Accordingly, it is possible to prevent the reflective layer28 from being exposed outwardly, thereby preventing deterioration of thereflective layer 28.

The current-spreading layer 33 covers the plurality of mesas M and thefirst conductive semiconductor layer 23. The current-spreading layer 33has openings 33 a which are positioned respectively in upper regions ofthe mesas M and expose the reflective electrodes 30 therethrough. Thecurrent-spreading layer 33 is also in ohmic contact with the firstconductive semiconductor layer 23, and is insulated from the pluralityof mesas M. The current-spreading layer 33 may include a reflectivemetal such as Al. Accordingly, in addition to light reflection caused bythe reflective electrodes 30, it is possible to obtain light reflectioncaused by the current-spreading layer 33. Thus, it is possible toreflect light that travels through side walls of the plurality of mesasM and the first conductive semiconductor layer 23.

The current-spreading layer 33 may be insulated from the plurality ofmesas M by the lower insulating layer 31. For example, the lowerinsulating layer 31 is positioned between the plurality of mesas M andthe current-spreading layer 33, so that the current-spreading layer 33can be insulated from the plurality of mesas M. The lower insulatinglayer 31 may have openings 31 b which are positioned respectively in theupper regions of the mesas M and expose the reflective electrodes 30therethrough, and may also have openings 31 a through which the firstconductive semiconductor layer 23 is exposed. The current-spreadinglayer 33 may be connected to the first conductive semiconductor layer 23through the openings 31 a. Each of the openings 31 b of the lowerinsulating layer 31 has an area narrower than that of each of theopenings 33 a of the current-spreading layer 33, and the openings 31 bare fully exposed by the openings 33 a.

The upper insulating layer 35 covers at least a portion of thecurrent-spreading layer 33. The upper insulating layer 35 has openings35 b for exposing the reflective electrodes 30 therethrough. Further,the upper insulating layer 35 may have an opening 35 a through which thecurrent-spreading layer 33 is exposed. The upper insulating layer 35 maycover side walls of the openings 33 a of the current-spreading layer 33.

The first pad 37 a may be positioned on the current-spreading layer 33.For example, the first pad 37 a may be connected to thecurrent-spreading layer 33 through the opening 35 a of the upperinsulating layer 35. The second pad 37 b is connected to the reflectiveelectrodes 30 through the openings 35 b of the upper insulating layer35. Upper ends of the first and second pads 37 a and 37 b may bepositioned at the same height as shown in FIG. 11. Thus, it is possibleto easily form a pad for connecting the reflective electrodes 30 exposedthrough the openings 35 a of the current-spreading layer 33.

According to an exemplary embodiment of the present invention, thecurrent-spreading layer 33 covers the mesas M and the substantiallyentire regions of the first conductive semiconductor layer 23 betweenthe mesas M. Thus, an electrical current can be easily distributedthrough the current-spreading layer 33. Since the current-spreadinglayer covers the plurality of mesas M and the first conductivesemiconductor layer 23, current-spreading performance is improvedthrough the current-spreading layer 33.

Further, the current-spreading layer 33 includes a layer of a reflectivemetal such as Al, or the lower insulating layer 31 is formed as aninsulating reflective layer, so that light not reflected by thereflective electrodes 30 can be reflected by the current-spreading layer33 or the lower insulating layer 31, thereby improving light extractionefficiency.

The flip-chip type LED chip according to this embodiment can have arelatively wide directivity distribution.

FIG. 13 shows graphs illustrating directivity distributions of theconventional LED package 200 and the light emitting device according toan exemplary embodiment of the present invention, i.e., the flip-chiptype LED chip 210 having a conformal coating layer.

Referring to FIG. 13( a), the conventional LED package 200 has a viewingangle of about 120 degrees. On the other hand, the light emitting deviceof the present exemplary embodiment has a viewing angle of about 145degrees as shown in FIG. 13( b). That is, it can be seen that thechip-level light emitting device according to an exemplary embodiment ofthe present invention has a viewing angle increased by 25 degrees ascompared with the conventional package-level light emitting device.

FIG. 14( a) shows a directivity distribution of a light emitting moduleusing the conventional LED package having a viewing angle of 120degrees, and FIG. 14( b) shows a directivity distribution of a lightemitting module using the flip-chip type LED chip 210 provided with theconformal coating layer having a viewing angle of 145 degrees accordingto an exemplary embodiment of the present invention. Here, a directivitydistribution of light in one axis direction was simulated using a lightemitting device and a lens having the same distribution of illuminationintensity in each direction. The directivity distribution of light showslight intensity depending on a viewing angle at a point spaced apart by5 m from each light emitting device. Here, the lower surface of the lenswas entirely flat without the inclination surface 310 b.

In these graphs, it is found that light is more widely and uniformlydistributed as an angle between maximum light intensities becomes largerand as a ratio (C/P) of a light intensity at the center to the maximumlight intensity becomes smaller. In FIG. 14( a), the angle between themaximum light intensities is 146 degrees, and the ratio of the lightintensity at the center to the maximum light intensity is 10%. In FIG.14( b), the angle and the ratio are 152 degrees and 4.5%, respectively.Upon comparison of angles at points with light intensity of 50%, theangle is 65 degrees in FIG. 14( a), and the angle is 70 degrees in FIG.14( b). Thus, in a case where a light emitting module is fabricatedusing the flip-chip type LED chip 210 having the conformal coating layeraccording to exemplary embodiments of the present invention, the lightemitting module according to exemplary embodiments of the presentinvention can more widely and uniformly distribute light than theconventional light emitting module.

FIGS. 15( a), (b) and (c) are schematic views illustrating exitdirections of light depending on various slopes of the inclinationsurface 310 b of the lower surface of the lens.

Beams of light exiting at angles, which were in a range of 0 to 3degrees with respect to the flat surface 310 a of the lower surface ofthe lens, below a side surface of the light emitting device 200 a weresimulated, and angles γ made between the beams of light exiting from thelens 300 a and the flat surface 310 a of the lower surface of the lenswere calculated.

In FIG. 15( a), an inclination angle β was about 4 degrees, and theangle γ of the beam of light exiting from the lens 300 a was 9 degrees.Therefore, the exit angle (90−γ) with respect to the central axis of thelens was 81 degrees.

In FIG. 15( b), the inclination angle β was about 9.5 degrees, and theangle γ of the beam of light exiting from the lens 300 a was 24 degrees.Therefore, the exit angle (90−γ) with respect to the central axis of thelens was 66 degrees.

In FIG. 15( c), the inclination angle β was about 23 degrees, and thebeam of light exiting from the lens 300 a underwent total internalreflection inside the lens 300 a and exited through an opposite sidesurface. In this case, the angle γ was 39 degrees. Therefore, the exitangle (90−γ) with respect to the central axis of the lens was 51degrees.

The angles γ of beams according to various inclination angles β of theinclination surface of the lower surface of the lens were calculated byperforming the aforementioned simulation with respect to the variousangles, and the calculated angles γ are shown in the graph of FIG. 16(a). The angles γ in the graph of FIG. 16( a) were converted into theexit angles (90−γ) of light, and the converted exit angles (90−γ) areshown in the graph of FIG. 16( b).

Referring to FIG. 16( a) or (b), it can be seen that as the inclinationangle β increases, the angle γ gradually increases, and that, in case ofthe inclination angle β exceeding about 20 degrees, the total internalreflection of light occurs inside the lens as shown in FIG. 15( c).Meanwhile, in a case where the inclination angle β is less than 5degrees, the angle γ gently increases as the inclination angle βincreases. However, in a case where the inclination angle β is 5 degreesor more, the angle γ relatively rapidly increases. In a case where theinclination angle β is 15 degrees or more, the angle γ converges into asubstantially straight line.

According to the results of the simulation described above, in case ofthe inclination angle β exceeding 20 degrees, the total internalreflection of light occurs inside the lens, thereby causing loss oflight. Since the exit angle (90−γ) is also less than 70 degrees, lightis focused near the central axis of the lens, thereby inhibitingachievement of uniform light.

Meanwhile, in a case where the inclination angle β is between 10 to 20degrees, the beam of light exits outwardly through the side surface ofthe lens without any total internal reflection. However, since the exitangle (90−γ) is less than 70 degrees, light is focused near the centralaxis of the lens, thereby inhibiting achievement of uniform light. Onthe other hand, in a case where the inclination angle β is less than 10degrees, the exit angle (90−γ) approximately exceeds 70 degrees, so thatlight can be preferably widely distributed.

Since flip-chip type LED chip is mounted directly on the circuit board,the size of the light emitting device can be decreased as compared witha conventional light emitting device using a package substrate.Accordingly, it is possible to slim the light emitting module. Further,since the size of the light emitting device 200 a is small, the size ofa concave portion 320 of the lens 300 a can be decreased. Furthermore,it is possible to decrease the entire height of the lens 300 a.

Although the present invention has been described in connection with thevarious exemplary embodiments, the present invention is not limited tothe specific exemplary embodiments. The elements of the specificexemplary embodiments described above can be identically or similarlyapplied to other exemplary embodiments unless they depart from thespirit of the present invention.

It will be apparent to those skilled in the art that variousmodifications and variation can be made in the present invention withoutdeparting from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A light-emitting module, comprising: a circuitboard; a light-emitting device disposed on the circuit board; and a lensdisposed on the circuit board, the lens configured to distribute lightemitted from the light-emitting device, wherein the lens comprises aconcave portion having an incidence surface configured to receive lightemitted from the light-emitting device, and wherein the light-emittingdevice is disposed within the concave portion of the lens.
 2. Thelight-emitting module of claim 1, wherein the light-emitting devicecomprises a chip-level light-emitting device.
 3. The light-emittingmodule of claim 2, wherein the chip-level light emitting device isdirectly mounted on the circuit board.
 4. The light-emitting module ofclaim 2, wherein the chip-level light-emitting device comprises: alight-emitting diode (LED) chip; and a wavelength conversion layerdisposed on the LED chip, wherein the wavelength conversion layer isdisposed on at least two surfaces of the LED chip.
 5. The light-emittingmodule of claim 1, wherein a width of an entrance of the concave portionof the lens is greater than a width of the light-emitting device.
 6. Thelight-emitting module of claim 5, wherein the width of the entrance ofthe concave portion of the lens is no more than two times greater thanthe width of the light-emitting device.
 7. The light-emitting module ofclaim 5, wherein the width of the entrance of the concave portion of thelens is no more than 3 mm.
 8. The light-emitting module of claim 1,wherein the lens comprises: a first surface comprising the concaveportion; and a second surface through which the light incident on theincidence surface of the concave portion exits.
 9. The light-emittingmodule of claim 8, wherein the incidence surface of the lens is an innersurface of the concave portion.
 10. The light-emitting module of claim9, wherein the incidence surface of the lens comprises an upper endsurface and a side surface continuing to an entrance of the concaveportion from the upper end surface.
 11. The light-emitting module ofclaim 10, wherein the concave portion comprises a shape narrowing as theconcave portion extends upward from the entrance of the concave portionto the upper end surface.
 12. The light-emitting module of claim 11,wherein the side surface comprises an inclination surface having aconstant slope from the entrance to the upper end surface, or the sidesurface comprises a curved inclination surface decreasing at a slopefrom the entrance to the upper end surface.
 13. The light-emittingmodule of claim 10, wherein the upper end surface comprises a flatsurface, a concave surface, or a convex surface.
 14. The light-emittingmodule of claim 10, wherein the upper end surface comprises alight-scattering pattern.
 15. The light-emitting module of claim 8,wherein the second surface of the lens comprises a concave surfacedisposed near a central axis of the lens, and a convex surface extendingfrom the concave surface.
 16. The light-emitting module of claim 8,wherein the second surface of the lens comprises a flat surface disposednear a central axis of the lens, and a convex surface extending from theflat surface.
 17. The light-emitting module of claim 8, wherein thefirst surface of the lens comprises a flat surface surrounding theconcave portion, and an inclination surface surrounding the flatsurface.
 18. The light-emitting module of claim 17, further comprising:a reflective sheet disposed on the circuit board.
 19. The light-emittingmodule of claim 17, wherein the inclination surface is inclined awayfrom the flat surface at a slope of approximately less than 10 degreeswith respect to the flat surface.
 20. The light-emitting module of claim17, wherein the lens further comprises leg portions disposed on theinclination surface, the leg portions of the lens being connected to thecircuit board.